Evaluación de los parámetros mecánicos de una … · Palabras Clave: Módulo resiliente, ley de...

Evaluation of mechanical parameters of an asphalt mixture underthe environmental conditions of Bogotá D.C.

Hugo Alexander Rondón Quintana*1, Fredy Alberto Reyes Lizcano**

Evaluación de los parámetros mecánicos de una mezcla asfálticasometida a las condiciones ambientales de la ciudad de BogotáD.C.

* Universidad Distrital Francisco José de Caldas, Bogotá D.C. COLOMBIA** Pontificia Universidad Javeriana. Bogotá D.C. COLOMBIA

Resumen

El artículo presenta el cambio que experimenta el módulo resiliente, la deformación permanente y la resistencia a fatiga de una mezcla de concreto asfálticocuando es expuesta a las condiciones climáticas de la ciudad de Bogotá D.C. (Colombia) durante 47-48 meses. Las mezclas fueron fabricadas utilizandodos cementos asfálticos (CA) fabricados en Colombia: CA 80-100 y CA 60-70. La tendencia general de las mezclas con el tiempo de exposición es experimentarun aumento en los valores de rigidez debido principalmente a procesos de endurecimiento por envejecimiento del ligante asfáltico. El aumento en rigidezgenera incremento en la resistencia al fenómeno de ahuellamiento y en la vida de fatiga de la mezcla analizada cuando ésta sea utilizada para conformarcapas asfálticas gruesas en el pavimento. Con base en la evolución del módulo resiliente con el tiempo de exposición al medio ambiente se propone unaecuación para predecir de manera aproximada el cambio que experimenta la vida a fatiga de la mezcla.

Palabras Clave: Módulo resiliente, ley de fatiga, envejecimiento, mezcla asfáltica densa en caliente, cemento asfáltico

Abstract

The present paper introduces the evolution of resilient modulus, permanent strain and fatigue life of an asphaltic concrete mixture exposed under weatherconditions in Bogota D.C. (Colombia) during 47-48 months. Mixtures were elaborated by using two asphaltic cements (CA) made in Colombia: CA 80-100 and CA 60-70. Mixtures generally tend to increase their stiffness values after an exposure period, mainly due to hardening and ageing processesundergone by asphaltic binder. A stiffness gain leads to increase endurance against rutting phenomenon and fatigue life of the analyzed mixture employedto lay thick asphaltic layers on the pavement. Based on the resilient modulus evolution due to exposure under environmental conditions, an equation isproposed to approximately predict the evolution of fatigue life endured by a mixture.

Keywords: Resilient modulus, fatigue law, aging, hot asphalt mixture, asphalt cement

Revista Ingeniería de Construcción Vol. 27 No1, Abril de 2012 www.ricuc.cl 57

1 Autor de correspondencia / Corresponding author:E-mail: [email protected]

1. Introducción 1. Introduction

Fecha de recepción: 22/ 08/ 2011Fecha de aceptación: 13/ 03/ 2012PAG. 57 - 74

Evaluación de los parámetros mecánicos de una mezcla asfáltica/Evaluation of mechanical parameters of an asphalt mixture

The main degradation mechanisms intended tobe controlled by empirical and mechanistic methodologiesof pavement design are fatigue and the excess of permanentdeformation on vertical road direction (rutting) (e.g., Shell,1978; TAI, 1982; AUSTROADS, 1992; AASHTO, 1993,TRL, 1993; HMSO, 1994; Urban Development Instituteand Universidad de Los Andes, 2002; MEPDG, 2004).Fatigue phenomenon caused by cyclic vehicular loadstake place inside bonded layers. In the case of flexiblestructures, this phenomenon takes place becauseof high deformation values due to tensile stress in thelowest area of an asphaltic layer. The continuous vehicletraffic makes the asphaltic layer bending down thusgenerating tensile stresses in its lower area.

58

Hugo Alexander Rondón Quintana, Fredy Alberto Reyes Lizcano

Revista Ingeniería de Construcción Vol. 27 No1, Abril de 2012 www.ricuc.cl

Such repeated load stress causes a stiffness loss of theasphaltic mixture and provokes plastic deformations dueto tensile stress, which in turn lead to micro-crackings.Because of continuous and repeated load stress andstiffness loss, micro-cracking coalescence takes placeleading to the occurrence of a visible cracking (macro-cracking). If the fatigue phenomenon occurs due to loadstress, macro-crackings take place in the lower area ofthe asphaltic layer (which is the area where the tensilestress is higher). Macro-crackings are spread upwards tothe road pavement surface where they are reflected asparallel crackings to the lengthwise carriage way direction,which under repeated traffic loads are spread creatingangular pieces that develop a map-cracking appearance.If this phenomenon takes place due to temperatureconditions, the crackings spreading effect occurs in theopposite way, thus micro-crackings are provoked fromthe grade line and they are spread towards the inner fiberin the asphaltic layer. On the other hand, rutting is theresidual vertical deformation accumulated due to trafficload, which may cause structural or functional failuresto the road pavement. In an asphaltic layer, thisphenomenon is mainly controlled by means of its ownmixture stiffness (dynamic or resilient modulus).

In Colombia there are few researches developedon asphaltic mixtures fatigue phenomena mainly becauseof the lack of appropriate equipment to conduct fieldand laboratory measurements and also due to a smallbudget for research purposes. Such situation explains thelack of knowledge on this subject and the lack of anappropriate model characterizing fatigue behavior frommaterial properties (mechanical, chemical, rheologicaland physical point of view), environmental conditionsand traffic behavior.

Generally, fatigue tests on asphaltic mixturesconsist in placing a specific geometric sample underrepeated and identical load stresses; in order to determinethe number of load cycles the sample is able to endure(Di Benedetto and De la Roche, 2005). This number ofload cycles endured before failure is known as fatigue-life. According to Epps and Monismith (1972), RaoTangella et al. (1990) and Di Benedetto et al. (2004) DiBenedetto and De la Roche (2005), the fatigue responsefrom asphaltic mixtures is mainly affected by:

59Revista Ingeniería de Construcción Vol. 27 No1, Abril de 2012 www.ricuc.cl


Sample compactation methods. Loading mode and the type of test applied. Mixture design parameters. Variants associated with the environment.

A detailed reference about fatigue phenomenonon asphaltic mixtures may be consulted from Gonzálezand Vásquez (2009).

On the other hand, the main factors affectingasphaltic mixtures durability, assuming they are properlyconstructed, are: ageing rate, and moisture damage (Airey,2003). Therefore, an asphaltic mixture must be designedand constructed not only to endure traffic loads but alsoenvironmental conditions. Evaluating the influence ofenvironmental conditions on this type of material behavioris not an easy task. Nowadays it is carried out by isolatingevery single component (water, temperature, ultra-violetrays, among others) to separately evaluate their influenceon binder and mixtures (from a mechanical and chemicalpoint of view) (Kemp and Predoehl, 1981; Welborn,1984; Kim et al., 1987; Shiau et al., 1991; Bishara et al.,2000; Bocci and Cerni, 2000; Brown and Scholz, 2000;Khalid and Walsh, 2000; Khalid, 2002; Airey, 2003; Said,2005; Shen et al., 2006). Additionally and generally,these researches employ test methods and equipment(e.g. thin-film-oven test TFOT, rolling-thin-film-oven testRTFOT, microwave ovens, automatic pressure agingvessels PAV), which can not fully reproduce the influenceof each environmental component on mechanical andrheological properties of mixtures and asphaltic binders(Jemison et al., 1991; Choquet and Verhasselt, 1992;Kuppens et al., 1997; Verhasselt, 1997). Furthermore,a significant amount of researches tend to combinethese tests and equipment to evaluate materialproperties changes under real environmental conditions(Jemison et al., 1991; Migliori and Corté, 1998; Montepara,1999; Montepara and Giuliani, 2000; Airey, 2003).As a general conclusion these test methodologies areunable to reproduce real conditions endured by asphalticmixtures in situ. A method to measure the environmentalinfluence on the behavior of asphaltic mixtures is bydeveloping segments test or tracks test at scale units.

60 Revista Ingeniería de Construcción Vol. 27 No1, Abril de 2012 www.ricuc.cl


The limitation of these tests is their high cost and theycan not directly or separately measure the influence oftraff ic loads and environmental conditions.

Consequently, this paper introduces a study thatintends to evaluate the influence of environmentalconditions in Bogota D.C (Colombia) on stiffness andfatigue strength of a dense hot asphaltic mixture typeMDC-2 (as per specifications by INVIAS, 2007 – RoadsNational Institute). It was decided to analyze this type ofmixture as it is commonly used to build tread layers,which are directly exposed to environmental conditions.In the same way, climatic conditions of Bogotá D.C. werechosen because the city is located in an area where thefollowing environmental conditions are present during agiven day: predominantly cold with minimum andmaximum average temperatures of 5°C and 19°C,respectively and; periodical rains at any moment in thesame day. In order to accurately understand theenvironmental influence on the behavior of asphalticmixtures, further researches will analyze different climateconditions. This paper introduces the results from the first47-48 months of the project, which evaluates mixtureselaborated with the two CAs produced in Colombia: CA60-70 and CA 80-100. Regarding climatic conditions,these binders are employed provided that yearly averagetemperature is higher and lower than 24°C, respectivelyin the area where the asphaltic layer will be built (INVIAS,2007).

In order to evaluate the environmental influenceon the mixture mechanical parameters, dynamiccharacterization tests were developed, such as resilientmodulus, permanent deformation strength and fatiguelaw. Fatigue tests were conducted under controlled stress.Table 1 summarizes the main differences observed betweentests under controlled stress and controlled deformation.


Tabla 1. Comparación de los ensayos bajo esfuerzo controlado y deformación controlada (Epps y Monismith, 1972;Di Benedetto y De la Roche, 2005)

Table 1. Comparison between tests under controlled stress and controlled deformation (Epps and Monismith, 1972;Di Benedetto and De la Roche, 2005)


Presently the investigation team, under adoctorate level study, is evaluating the effect of eachcomponent of Bogota environmental conditions and theloads on the mixture chosen for this research. For thisteam it was important to get acquainted with the behaviorof every environmental component, in order to clearlydescribe and understand the results provided by microlevel studies (isolated components).

2. Methodology

Design of asphaltic mixtures and characterization ofmaterials. The quarry rock aggregate used for theelaboration of asphaltic mixtures to be employed inMarshall Test (called briquettes) comes from “Subachoque”quarry (Cundinamarca, Colombia). The following testswere conducted on such materials, in accordance withspecifications by the Roads National Institute (2007a):grading analysis on coarse and fine aggregates (INV. E-213), fine aggregates absorption and specific weight (INV.E-222), coarse aggregates absorption and specific weight(INV. E-223), aggregates abrasion resistance (sizes lowerthan 3/4”) by employing the Los Angeles apparatus (INV.E-218); Micro-Deval abrasion test (INV.E-238), strengthloss test (INV.E-220), fractured particles (INV. E – 227),

Parámetro/Parameter

Evolución durante el ensayo

Evolution during the test

Criterio usual de falla

Usual failure criterion

Vida a la fatiga

Fatigue-life

Dispersión de los resultados

Dispersion of results

Aumento de la temperatura

Temperature increase

Aumento del modulo de rigidez

Stiffness modulus increase

Efecto del tiempo de receso

Effect of recess time

Duración de la propagación de las macro-fisuras

Macro-cracking spreading duration

Crecimiento del daño

Damage growth

Esfuerzo controlado/Controlled stress

Aumento de la deformación

Deformation increase

Rotura de la muestra

Sample rupture

Más corta

Shorter

Más baja

Lower

Disminución de la vida

Life decrease

Aumento de la vida

Life increase

Mayor efecto benéfico

Greater benign effect

Corta

Short

Más rápido de lo que ocurre in situ

Faster than in situ

Deformación controlada/Controlled deformation

Disminución del Esfuerzo

Stress decrease

Perdida de la mitad del esfuerzo inicial

Loss of half initial stress

Más larga

Longer

Más alta

Higher

Aumento de la vida

Life increase

Disminución de la vida

Life decrease

Menor efecto benéfico

Lower benign effect

Larga

Long

Más representativo de lo que ocurre in situ

More representative than in situ


Tabla 2. Caracterización de los agregadosTable 2. Aggregates Characterization


test to measure sand content (INV. E – 133) and elongation- flattening indexes (INV. E-230). These test results arepresented in table 2, which values meet the minimumquality standards established by INVIAS (2007)specifications for the elaboration of MDC-2 mixtures usedfor tread layers construction.

In order to characterize mixtures the followingstandard tests were conducted on asphaltic cements CA80-100 and CA 60-70 according to (INVIAS 2007)specifications: penetration (ASTM D-5), dynamic viscosity(ASTM D-4402), ductility (ASTM D-113), solubility intrichloroethylene (ASTM D-2042), water content (ASTMD-95), softening point (INV. E-712), residual analysisafter rolling-thin-film-oven test (RTFOT) ASTM D-2872).These tests results are presented in Tables 3 and 4.

After analyzing tests conducted on quarryrock aggregates and on asphaltic cements, fivebriquettes were elaborated (compacted with 75 strikesper face) for each asphalt percentage between 4.5%and 6.5%, in order to develop Marshal Design (INV. E-748, INVIAS, 2007a), so as to determine the optimumasphalt content of the mixture. In order to meet INVIAS(2007) specifications and to elaborate asphalt mixturestype MDC-2, the original aggregates grading was modifiedby using as a reference the percentage averagevalues from grading range, established by thespecification for briquettes elaboration for Marshall Test.

Ensayo/Test

Peso específicoSpecific weightEquivalente de arenaSand ContentCaras fracturadasFractured facesÍndice de alargamientoElongation indexÍndice de aplanamientoFlattening indexAtaque en Sulfato de sodioSodium sulfate attackMicrodevalMicrodevalResistencia al desgaste máquina de los ÁngelesAbrasion resistance Los Ángeles apparatus

Resultado/Result

2.56

86%

92%

10%

10%

12.4%

20.3%

22.5%


Tabla 3. Características generales del cemento asfálticoTable 3. General Characteristics of CA 80-100 asphaltic cement

Tabla 4. Características generales del cemento asfálticoTable 4. General Characteristics of CA 60-70 asphaltic cement


Ensayo/Test

Penetración (25°C, 100 g, 5 s)Penetration (25°C, 100 g, 5 s)Índice de penetraciónPenetration indexViscosidad absoluta (60°C)Dynamic viscosity (60°C)Ductilidad (25°C, 5cm/min)Ductility (25°C, 5cm/min)Solubilidad en TricloroetilenoTrichloroethylene solubilityContenido de aguaWater contentPunto de inflamación COCFlashpoint COC

Pérdida de masaMass lossPenetración (25°C, 100 g, 5 s)Penetration (25°C, 100 g, 5 s)

Método/Method

ASTM D-5

INV. E-724

ASTM D-4402

ASTM D-113

ASTM D-2042

ASTM D-95

ASTM D-92

ASTM D-2872

ASTM D-5

Unidad/Unit

0.1 mm

-

Poises

cm

%

%

°C

%

%

CA 80-100

80-100

-1/+1

1000 mín.

100 mín.

99 mín.

0.2 máx.

232 mín.

1.0 máx.

48 mín.

Resultado/Result

85

-0.5

1400

>105

>99

<0.2

295

0.2

65

Ensayos sobre el asfalto originalTests developed on original asphalt

Ensayos sobre el residuo luego del RTFOTTest developed on residue after RTFOT

Ensayo/Test

Penetración (25°C, 100 g, 5 s)Penetration (25°C, 100 g, 5 s)Índice de penetraciónPenetration indexViscosidad absoluta (60°C)Dynamic viscosity (60°C)Ductilidad (25°C, 5cm/min)Ductility (25°C, 5cm/min)Solubilidad en TricloroetilenoTrichloroethylene solubilityContenido de aguaWater contentPunto de inflamación COCFlashpoint COC

Pérdida de masaMass lossPenetración (25°C, 100 g, 5 s)Penetration (25°C, 100 g, 5 s)

Método/Method

ASTM D-5

INV. E-724

ASTM D-4402

ASTM D-113

ASTM D-2042

ASTM D-95

ASTM D-92

ASTM D-2872

ASTM D-5

Unidad/Unit

0.1 mm

-

Poises

cm

%

%

°C

%

%

CA 60-70

60-70

-1/+1

1500 mín.

100 mín.

99 mín.

0.2 máx.

232 mín.

1.0 máx.

52 mín.

Resultado/Result

67

-0.7

1750

>105

>99

<0.2

275

0.4

70

Ensayos sobre el asfalto originalTests developed on original asphalt

Ensayos sobre el residuo luego del RTFOTTest developed on residue after RTFOT

Calculations obtained from Marshall Test are registeredin Tables 5 and 6. The optimum percentages of asphalticcements, according to data in tables 5 and 6, are 5.3%and 5.6% for mixtures elaborated with CA 80-100 andCA 60-70, respectively. These percentages meet theminimum requirements established by INVIAS (2007)specification for MDC-2 and traffic types NT1 and/orNT2 (low and medium traffic volumes).


Tabla 5. Resumen del ensayo Marshall para mezcla asfáltica MDC-2 con CA 80-100Table 5. Summary of Marshall Test for MDC-2 asphaltic mixture containing CA 80-100

Tabla 6. Resumen ensayo Marshall para mezcla asfáltica MDC-2 con CA 60-70Table 6. Summary of Marshall Test for MDC-2 asphaltic mixture containing CA 60-70


CA

[%]

4.5

5.0

5.5

6.0

Peso unitario

Unit weight

[g/cm3]

2.21

2.24

2.24

2.23

Estabilidad

Stability

(E) [kg]

710

835

853

813

Vacíos en la mezcla

Mixture Voids

[%]

7.63

5.76

5.09

4.64

Vacíos en agregados

Aggregates Voids

[%]

17.52

16.89

17.33

17.96

Flujo (F)

Flow

[mm]

3.33

3.45

3.51

3.70

Relación

Relation

E/F [kg/mm]

213.09

242.14

243.48

219.71

CA

[%]

5.0

5.5

6.0

6.5

Peso unitario

Unit weight

[g/cm3]

2.24

2.25

2.25

2.26

Estabilidad

Stability

(E) [kg]

1189

1323

1393

1229

Vacíos en la mezcla

Mixture Voids

[%]

5.83

4.47

3.48

3.02

Vacíos en agregados

Aggregates Voids

[%]

16.95

16.80

16.96

17.60

Flujo (F)

Flow

[mm]

3.40

3.60

3.69

3.92

Relación

Relation

E/F [kg/mm]

349.86

367.84

377.18

313.38

Development phase. After applying Marshall Design,briquettes were elaborated (180 each per type of CA)with asphaltic mixture MDC-2 to be exposed underBogota D.C environmental conditions, employing theoptimum CA content. These samples were placed on abuilding roof in Bogota D.C.

During the first 47-48 months of the Project,every three months resilient tests and permanentdeformation tests were developed on these briquettes, inorder to evaluate the parameters evolution in relation toenvironmental exposure periods. Resilient modulus test(INV. E-749, INVIAS, 2007a) has been developed at threedifferent temperatures (10, 20 and 30°C), and loadfrequencies (2.5, 5.0 and 10.0 Hz) by using the NottinghamAsphalt Tester (NAT). The permanent deformationresistance test, under repeated load cycles, was conductedunder 100 kPa stress at 3600 load cycles in accordancewith standard procedure by EN 12697-22 (CEN, 2005).By using these tests results, an empirical equation wasdeveloped in order to predict the strength evolution ofthe analyzed mixture, in relation to the exposure timeperiod to environmental conditions.



So as to evaluate environmental conditions influence ofBogota D.C. on fatigue strength in the studied mixture,two phases were developed.

1. Phase 1: 360 fatigue tests and resilient modulus wereanalyzed on asphaltic concrete mixtures type MDC-1,MDC-2 and MDC-3 (developed in accordance withINVIAS, 2007), which were elaborated with CA 80-100 mixture. This analysis was developed in order todetermine the evolution of mixtures fatigue strengthunder stiffness. Fatigue results were obtained byconducting tests with the indirect tensile method usinga NAT apparatus, following the procedures establishedby the prEN 12697-24E (CEN, 2005) specification. Thetest temperature and load frequency were 20°C and2.5 Hz, respectively. Load type selected for this testwas controlled stress. Samples dimensions for fatiguetests are the same as those in Marshall Briquettes.

The results from this phase were used to developan empirical equation that relates the evolutionundergone by fatigue-life of asphaltic concrete mixturesunder stiffness.

2. Phase 2: By employing the equation developed fromphase 1 results, and based on data from stiffnessevolution of time-exposed MDC-2 mixture underenvironmental conditions, the fatigue strength increaseendured by such mixture when exposed at climateconditions in Bogota D.C. was determined quiteaccurately.

3. Results

Figures 1a-b present the evolution of initialresilient modulus (Eo, in MPa) of MDC-2 mixture(elaborated with CA 80-100 and CA 60-70, respectively)at temperature (T, in °C) and frequency load (F, in Hz). Atypical modulus increase is observed when load frequencyis increased and temperature decreases in the test. Thisevolution may be mathematically represented by meansof the empirical Equation (1). In order to employ thisequation, it is necessary to identify six status variantsobtained by means of regressions. In the case of theanalyzed mixture, these variants are presented in Table 7.


Tabla 7. Variables para simular la rigidez de la mezcla MDC-2 en función de T y FTable 7. Variants used to simulate MDC-2 mixture stiffness in function of T and F

Figura 1. Evolución del módulo resiliente inicial (Eo) de la mezcla MDC-2 con la temperatura (T) y la frecuencia de carga (F).Mezcla fabricada con a) CA 80-100 y b) CA 60-70

Figure 1. Evolution of initial resilient modulus (Eo) of MDC-2 mixture at temperature (T) and load frequency (F).Mixture elaborated from a) CA 80-100 y b) CA 60-70


These variants do not deliver a defined physical meaningand they mainly change with the type of binder, gradingand type of rock aggregate employed in the elaborationof mixtures. Load frequency F in the Equation (1) maybe translated as the vehicle speed (V, in cm/s) by meansof equation (2) proposed by Lin (1989, 1989a).

tc is loading time expressed in seconds for an in-motionvehicle at different depths (h in cms and measured fromthe pavement structure surface) and L is the wheel rimlength in contact with the road pavement (usually 30cms).

(1)

(2)

CA

80-100

60-70

a

8.78

9.21

b

-0.0035

-0.00214

c

5.26

3.4

d

-0.63

-0.31

e

12.4

14.9

f

-1.75e-4

-1.5e-4

a) b)Frecuency Frecuency


Figura 2. Evolución del módulo resiliente (E) con el tiempo de envejecimiento (t) para mezclas fabricadas con a) CA 80-100 y b) CA 60-70Figure 2. Evolution of resilient modulus (E) throughout ageing time (t) for mixtures elaborated from a) CA 80-100 and b) CA 60-70

Figura 3. Evolución de la deformación vertical permanente con el tiempo de envejecimiento (t)para mezclas fabricadas con CA 80-100 y CA 60-70

Figure 3. Evolution of vertical permanent deformation throughout ageing time (t)for mixtures elaborated from CA 80-100 and CA 60-70


Figure 2 indicates the evolution of resilientmodulus for asphaltic mixtures throughout time. Mixturesfabricated from CA 80-100 and CA 60-70 (Figures 2a andb, respectively) show a typical modulus increase whenload frequency is incremented and test temperature isdecreased. In mixtures fabricated from CA 80-100, themodulus tends to increase throughout exposure timeunder environmental conditions (see Figure 2a) and,therefore, permanent deformation strength increases(Figure 3). Such phenomenon takes place mainly due tooxidative ageing experimented by asphaltic cements dueto temperature and ultra-violet (UV) radiation exposureeffects.

a) b)

Vert

ical

per

man

ent d

efor

mat

ion



Mixtures fabricated from CA 60-70 experimenta different behavior in comparison to those fabricatedfrom CA 80-100 (see Figures 2b and 3). During the firstexposure months, the mixtures decrease their modulusby increasing permanent deformations. Afterwards suchmodulus is stabilized and finally there is an increasingtendency to decrease deformation values (especiallywhen the test is developed at temperatures ranging from20 to 30°C). Probably the modulus decay is produced bymicro-cracking generation, which appears at lowtemperatures when mixtures are too rigid (fragile behavior).Then those micro-cracking are stabilized and the stiffnessincreases due to an ageing and asphalt oxidativephenomenon similar to the one taking place in CA 80-100 mixtures. Micro-cracking phenomenon at lowtemperatures has been widely studied by severalresearchers (e.g., Kliewer et al., 1996; Sebaaly et al.,2002; Nesnas and Nunn, 2006).

Water effect is not clear from observed results,since mixture humidity produces de-bonding betweenrock aggregate and asphalt; probably provoking a modulusdecrease and mechanical resistance drop. Additionalresearchers in this field shall be conducted.

Figure 4 presents the relation (E/Eo) betweenresilient modulus obtained after exposing briquettes underenvironmental conditions during different periods of time(E) and, the initial mixtures resilient modulus for a periodof t=0 months (Eo). In the case of mixtures elaboratedfrom CA 80-100, the modulus obtained from t=48increases from 48 to 176%, in relation to the initialmodulus (depending on the temperature and frequencyof the test). The most significant increment is observedas long as temperature increases in the test. CA 60-70mixtures experiment a maximum modulus decrease of35% during the first five months of exposure. However,after t=47 months, these mixtures increase and experimentmodulus that slightly supersede the initial value.These results can be mathematically expressed bymeans of equations (3a) and (3b) for CA 80-100 andCA 60-70 asphaltic mixtures. This equation can onlybe employed for the analyzed mixture in the periodof time under analysis (47-48 months), because themixture behavior might change as long as t increases. Aswell as in equation (1), in equation (3) the status variants k1-k3 are obtained by means of regressions and do notprovide a defined physical meaning (see Table 8).


Figura 4. Evolución de la relación entre el módulo resiliente (E) y el módulo inicial (Eo) con el tiempo de envejecimiento (t)Figure 4. Evolution of relation between resilient modulus (E) and initial modulus (Eo) throughout ageing time (t)

para/for CA 80-100 (3a)

para/for CA 60-70 (3b)

para/for CA 80-100 (4a)

para/for CA 60-70 (4b)

Tabla 8. Variables para simular la rigidez de la mezcla MDC-2 en función del tiempo de exposición al medio ambienteTabla 8. Variants used to simulate mixture MDC-2 stiffness, in function of exposure time under environmental conditions


CA

80-100

60-70

k1

0.17

0.058

k2

-

-0.012

k3

-

0.058

Regression empirical equations that might reproduce theevolution of resilient modulus throughout time of exposureunder environmental conditions, are enunciated in (4a)and (4b) for CA 80-100 and CA 60-70 mixtures,respectively. Such Equations are formulated based on theequations (1) and (3). Figure 4 presents the simulation ofexecuted tests employing the equations (4a-b) and thecorrelation coefficient is r2=0.79.


Figura 5. Evolución de max con EFigure 5. Evolution of max with E


(5)

(6)

Figure 5a presents the results from fatigue testingdeveloped on 360 samples of asphaltic concrete typeMDC-1, MDC-3 and MDC-3. There is an amplitude valuedecrease max (deformation amplitude for material failurewhen Nf load cycles are applied) as long as resilientmodulus is incremented in mixtures (E), which isequivalent to the status where the material is changingits behavior from ductile to fragile due to stiffening. Theseresults can be mathematically represented by means ofEquation (5). This equation was chosen taking intoconsideration that for a very low level of deformationamplitude applied on the material, it can endure suchamplitude infinite times without rupturing (concept offatigue endurance limit stated by Carpenter et al., 2003and Reyes, 2003). Status variant values in the equation(5) were determined by means of regression: k4=6.24x10-6, k5=0.48 and k6=15.79. Similar results as the ones foundin this research were reported by Schmidt and Santucci(1969). Although material allows lower tensiledeformations as long as it stiffens, fatigue-life or thenumber of cycles required for material failure (Nf) increases,as described by equation (6) (see figure 6). Such resultsare in accordance with those reported by the referredbiography.


Figura 6. Evolución del número de ciclos de falla con /EFigure 6. Evolution of number of failure cycles with /E


If equations (4-5) are fused, the evolutionexperimented by ?max with the evolution of mixturesstiffness exposed to environmental conditions in BogotaD.C. are obtained. By using these equations it is possibleto predict that acceptable tensile deformation of themixture will decrease from tinicial=0 up to t=29 months,from 55 to 64%, only due to the effect of increasedstiffness during exposure to environmental conditions inBogota D.C. In the same way, during the same period oftime the equation (6) reports an average increase offatigue-life 6.85 times higher, due to the mixture stiffeningeffect. From t=30 up to t=48 months, stiffening effectdecreases and the mixture will experiment a fatigue-lifeincrease of 10 times, due to stiffening from tinicial=0 upto tinicial=48 months.

The analysis of fatigue-life for CA 60-70 mixturesis far more complex, since during the first exposuremonths under environmental conditions, stiffness dropsin an average of 12.8 % causing a reduction of 33 % inthe mixture fatigue-life. However, between t=5 andtfinal = 47 months, it reappears and increases stiffness,thus generating at the end of exposure time a slightaverage increment of fatigue-life of 38 % in comparisonto tinicial = 0 months.


5. Referencias / References


4. Conclusions

This study conducted a development phaseintended to measure the influence of climatic conditionsin Bogota D.C, on the stiffness and fatigue-life of anasphaltic concrete mixture type MDC-2 elaborated fromasphaltic cement type CA 80-100 and CA 60-70. Fromobtained results it is concluded that resilient modulus ofthe CA 80-100 mixture increases an average of 2.17times, during 48 months of exposure under environmentalconditions. Such stiffness increase generates an incrementof approximately 10 times in mixture fatigue-life, onlybecause of asphaltic binder stiffening effect, due to itsown ageing condition. In the case of CA 60-70 mixtures,the increment of fatigue-life during 47 exposure monthswas only of 38%, since during the first 5 months suchproperty decreased probably due to thermal micro-cracking endured by the mixture at low temperatures.The mixtures stiffness increment created an obviousendurance increase against rutting phenomenon.

Fatigue results previously introduced are validprovided that the analyzed mixture is made of thickasphaltic layers, where controlled stress is the loadingmode. These results are also valid for pavements exposedonly under environmental conditions and during theanalyzed period of time. Presently the research group isjointly evaluating the loading effects, the modification ofbinder chemical composition and the environmentalconditions to clearly understand the evolution of damagemechanisms on asphaltic layers.

AASHTO (1993), American Association of State Highway and Transportation Officials, Guide for design of pavement structures.Washington, D.C.

Airey G. D. (2003), State of the art report on ageing test methodgs for bituminous pavement materials. International Journal ofPavement Engineering, Vol. 4, No 3, 165-176.

Austroads (1992), Pavement design, a guide to the structural design of road pavement. Austroads, Sydney, Australia.Bishara S. W., Robertson R. E. and Mahoney D. (2000), Rapid oxidative aging of binder using microwave energy - an improved

method. In Proc. 2nd Eurasphalt and Eurobitume Congress, Session 2: Development in Bituminous Products and Techniques,(Barcelona), 27-36.

Bocci M. and Cerni G. (2000), The ultraviolet radiation in short-and long-term aging of bitumen. In: Proc. 2nd Eurasphalt andEurobitume Congress, Session 1: Performance Testing and Specifications for Binder and Mixtures (Barcelona), 49-58.

Brown S. F. and Scholz T. V. (2000), Development of laboratory protocols for the ageing of asphalt mixtures. In: Proc. 2ndEurasphalt and Eurobitume Congress, Session 1: Performance Testing and Specifications for Binder and Mixtures, (Barcelona),83-90.



Carpenter S. H., Ghuzlan K. A. and Shen S. (2003), Fatigue endurance limit for highway and airport pavement. TransportationResearch Record (TRR): Journal of the Transportation Research Board, No. 1832, TRB, National Research Council, WashingtonD.C, 131-138.

CEN (2005), Committee European of Normalization. Bituminous Mixture Test Methods for Hot Mix Asphalts - Part25: CyclicCompression Tests.

Choquet F. S. and Verhasselt A. F. (1992), Natural and accelerated ageing of bitumens - effects on the asphaltenes. In: Proc. ofan International Symposium on Asphaltene Particles in Fossil Fuel Exploration, Recovery, Refining and Production Processes,Ed. MK Sharna and TF Yen 1994, Plenum Press, New York, 13-29.

Di Benedetto H. and De la Roche C. (2005), State of the art on stiffness modulus and fatigue of bituminous mixtures. ReportRILEM No. 17 Bituminous binders and mixes: State of the art and interlaboratory test on mechanical behavior and mix design,L. Francken, ed., E and FN Spon, London, 2005, pp. 97-123.

Di Benedetto H., De la Roche C., Baaj H., Pronk,A. and Lundstrom R. (2004), Fatigue of bituminous mixtures. Material andStructures, Vol. 37, No. 4, 202-216.

Epps J. A. (1969), Influence of mixture variables on the flexural fatigue and tensile properties of asphalt concrete. Ph. D. thesis,University of California, Berkeley, Calif.

Epps J. A. and Monismith C. L. (1972), Fatigue of asphalt concrete mixtures - summary of existing information. Fatigue ofCompacted Bituminous Aggregate Mixtures, ASTM STP 508, American Society for Testing and Materials, 19-45.

González L. A. and Vásquez S. E. (2009), Estado del conocimiento sobre el fenómeno de fatiga en mezclas asfálticas. Tesis depregrado, Universidad Católica de Colombia, Bogotá D.C. (Colombia).

Harvey J. and Tsai B.-W. (1997), Long-term oven aging effects on fatigue and initial stiffness of asphalt concrete. TransportationResearch Record (TRR): Journal of the Transportation Research Board, No. 1590, 89-98.

HMSO (1994), DMRB-Design Manual for Roads and Bridges. Vol. 7, HD 25/94, part 2, Foundations.Instituto de Desarrollo Urbano y Universidad de Los Andes. (2002). Manual de Diseño de Pavimentos para Bogotá. Bogotá D.C.,

Colombia.INVIAS (2007), Instituto Nacional de Vías. Especificaciones Generales para Construcción de Carreteras. Bogotá D.C., Colombia.INVIAS (2007a), Instituto Nacional de Vías. Normas de Ensayos de Materiales para Carreteras. V. I y II. Bogotá D.C., Colombia.Jemison, H. B., Davison, R. R., Glover, C. J. and Bullin, J. A. (1991). Evaluation of standard oven tests for hot-mix plant aging.

Transportation Research Record, 1323, Transportation Research Board, Washington D.C., 77-84.Kemp G. R. and Predoehl N. H. (1981), A comparison of field and laboratory environments of asphalt durability. Proc. Assn.

Asphalt Paving Technol., 50, 492-537.Khalid H. A. (2002), A new approach for the accelerated ageing of porous asphalt mixtures. Proceedings of the Institution of Civil

Engineers, Transport 153, Issue 3, 171-181.Khalid H. A. and Walsh C. M. (2000), Relating mix and binder fundamental properties of aged porous asphalt materials. In: Proc.

2nd Eurasphalt and Eurobitume Congress, Session 1: Performance Testing and Specifications for Binder and Mixtures (Barcelona),398-405.

Kim O-K., Bell C. A., Wilson J. E. and Boyle G. (1987), Development of laboratory oxidative aging procedures for asphalt cementsand asphalt mixtures. Transportation Research Record, 1115, Transportation Research Board, Washington D.C., 101-112.

Kliewer J. E., Zeng H. and Vinson T. S. (1996), Aging and low-temperature cracking of asphalt concrete mixture. Journal of ColdRegions Engineering, Vol. 10, No. 3, 134-148.

Kuppens E. A. M., Sanches F., Nardelli L. and Jongmans E. C. (1997), Bitumen-ageing tests for predicting durability of porousasphalt. In: Di Benedetto, H., Francken, L., Proc. Fifth International RILEM Symposium, Mechanical Tests for BituminousMaterials, 71-77.

Lin X. X. A (1989), Method of Determining the Relevant Parameters in the Calculation of Pavement Deformation of BituminousSurface. China J. Highway and Transport, No. 2, 10-20.

Lin X. X. (1989a), Study on Semi-Rigid Asphalt Pavement. Rep. of Key Sci. and Tech. Projects 85-65, Ministry of Communications,Beijing.

MEPDG. ARA, Inc. ERES Consultants Division (2004), Guide for the Mechanistic-Empirical Design of New and RehabilitatedPavement Structures. NCHRP Project 1-37A, Transportation Research Board, Washington, D.C., www.trb.org/mepdg/. AccessedSeptember 12 of 2007.

Migliori F. and Corté J-F. (1998), Comparative study of RTFOT and PAV aging simulation laboratory tests. Transportation ResearchRecord, 1638, Transportation Research Board, Washington D.C., 56-63.

Montepara A. (1999), A theoretical-interpretative model of the relationship between UV-radiation ageing of bitumen and viscosityvariation. In: Proc. of Eurobitume Workshop, paper No. 075, Luxemburg.

Montepara A. and Giuliani F. (2000), Comparison between ageing simulation tests of road bitumen. In: Proc. 2nd Eurasphaltand Eurobitume Congress, Session 1: Performance Testing and Specifications for Binder and Mixtures, (Barcelona), 518-523.



Nesnas K. and Nunn M. E. (2006), A thermal pavement response model for top-down reflection cracking in composite pavements.In 85th Annual Meeting of the Transportation Research Board, paper No. 06-0127, Washington, D.C., January 2006.

Rao Tangella R., Craus J., Deacon J. A. and Monismith C. L. (1990), Summary report on fatigue response of asphalt mixtures.Rep. to Strategic Highway Research Program, Washington, D.C.

Reyes F. A. (2003), Diseño Racional de Pavimentos. Escuela Colombiana de Ingeniería, 1ra. Edición, Bogotá D.C., Colombia.Said S. F. (2005), Aging effect on mechanical characteristics of bituminous mixtures. Transportation Research Record: Journal of

the Transportation Research Board, 1901, Washington D.C., 1-9.Schmidt R. J. and Santucci L. E. (1969), The effect of asphalt properties on the fatigue cracking of asphalt concrete on the Zaca-

Wigmoretest Project. In: Proceedings, Association of Asphalt Paving Technologists, PRPTA, Vol. 38, 39-64.Sebaaly P. E., Lake A. and Epps J. (2002), Evaluation of low-temperature properties of HMA mixtures. Journal of Transportation

Engineering, Vol. 128, No. 6, 578-586.SHELL (1978), International Petroleum Company. Shell Pavement Design Manual, Asphalt Pavement and Overlays for Road Traffic.

London (U.K.).Shen J., Amirkhanian S. and Tang B. (2006), Influence of accelerated aging test temperature on the properties of binders.

International Journal of Pavement Engineering, Vol. 7, Issue 3, 191-198.Shiau J-M., Tia M., Ruth B. E. and Page G. C. (1991), Characterization of age-hardening potential of asphalt by using Corbett-

Swarbrick asphalt fractionation test. Transportation Research Record, 1323, Transportation Research Board, Washington D.C.,53-60.

TAI-The Asphalt Institute (1982), Research and Development of the Asphalt Institutes Thickness Design Manual. MS 1, 9th Ed.College Park, Md.

TRL-Transport Research Laboratory (1993), A guide to the structural design of bitumen surfaced roads in tropical and subtropicalcountries. Draft 4th edition.

Verhasselt A. F. (1997), Field ageing of bituminous binders: simulation and kinetic approach. In: Di Benedetto, H., Francken,L., Proc. Fifth International RILEM Symposium, Mechanical Tests for Bituminous Materials, 121-128.

Welborn J. Y. (1984), Physical properties as related to asphalt durability: state of the art. Transportation Research Record, 999,Transportation Research Board, Washington D.C., 31-36.

Evaluación de los parámetros mecánicos de una … · Palabras Clave: Módulo resiliente, ley de...

Documents

Transcript of Evaluación de los parámetros mecánicos de una … · Palabras Clave: Módulo resiliente, ley de...